DE 10 2007 024 777 A1 shows a roller hemming device, which has a horizontal hemming bed with laterally arranged hemming robots, which hem the flanges of the workpiece together with roller hemming heads, wherein the hemming bed additionally rotates by means of an axis of rotation of its own. The hemming robots hem outer flanges of the workpiece and both act on the front side of the workpiece.
If a workpiece, e.g., a vehicle door, has inner and outer flanges or lock seams, which are accessible and hemmed from different main sides of the workpiece, especially from the front side and the rear side of the workpiece, there is in practice a change from one station to another, with the workpiece being picked up after hemming one flange, e.g., the outer flange, and transported to a next hemming device in order to hem the other, e.g., inner flange there.